Aperture devices including a multiplicity of aperture elements for the variable delimitation of the cross section of a ray bundle running through an optical system are known, for example, in the form of aperture stops for optical imaging systems. Aperture stops are used to set the numerical aperture—effectively used for an imaging—of the optical system for the corresponding application by virtue of the fact that the cross section of the ray bundle is delimited in a defined manner in the region of a pupil surface of the optical system and the angular spectrum of the rays impinging in the image field is defined thereby. If the optical system is optionally intended to be operated with different numerical apertures, then a variable delimitation of the ray bundle cross section is desired.
Variable aperture devices in the form of iris diaphragms are known which have a plurality of lamellar, generally crescent-shaped aperture elements, which can be jointly rotated inward or outward via a mechanism in order to set the size of the more or less circular effective aperture opening jointly defined by all the lamellae.
Aperture devices are also known which have a plurality of aperture elements which can in each case be moved between an engagement position in the beam path of the optical system and a neutral position outside the beam path of the optical system and in each case have an aperture opening delimited by an aperture edge.
WO 2005/050322 A1 (corresponding to US 2007/0053076 A1) discloses diaphragm changing devices for a projection objective operating with electromagnetic radiation from the extreme ultraviolet range (EUV). The diaphragm changer has a diaphragm store with a plurality of substantially disk-shaped aperture elements which in each case have an aperture openings of fixed shape and size and which can optionally be introduced into an aperture position directly in front of a concave mirror of the projection objective or be removed from this aperture position with the aid of the diaphragm changer. The aperture elements are accommodated within a magazine in separate inserts and, with the aid of a movable robot gripper arm, are removed from the corresponding separate insert, introduced into the beam path and, after they have been used, deposited in the magazine again.
WO 2007/105549 A1 discloses aperture devices having one or a plurality of aperture elements which are in each case pivotable about a rotation axis with the aid of a pivoting drive between an engagement position in the beam path of the system and a neutral position outside the beam path of the optical system and which in each case have an aperture opening of defined form and size delimited by an aperture edge. In the case of embodiments having a plurality of pivotable aperture elements, firstly an aperture element having a larger aperture opening is pivoted into the engagement position and, as desired, subsequently an aperture element having a smaller aperture opening, wherein the aperture element having the larger aperture opening can remain in its neutral position, such that the aperture element having the smaller aperture opening defines the effective aperture opening. The aperture elements having smaller aperture openings in this case each have an outer section and an inner section, which projects conically relative to the outer section and which delimits the smaller aperture opening in this dimension in such a way that it can be introduced into the larger aperture opening in such a way that the smaller aperture opening, in its neutral position, lies in the same plane as the larger aperture opening already lying in the engagement position. The effect of an adjustable planar aperture is thereby achieved with the aid of foldable aperture elements.
A further aperture device including pivotable aperture elements is known from U.S. Pat. No. 4,675,590. The aperture device is part of a laser processing machine and serves for setting the transverse mode distribution of the laser beam in a variable fashion as desired. For this purpose, the aperture device has a stationary aperture element, which is fixedly installed within the laser resonator, and also one or a plurality of aperture elements which can be swung selectively into the beam path of the laser resonator in addition to the stationary aperture element and the aperture openings of which are smaller than the aperture opening of the stationary aperture element. The aperture element respectively swung into the engagement position defines, with its aperture opening, the effective active aperture opening.